Résumé
The success of silica-based optical fibers are many: transmission fibers and fiber amplifiers for telecommunications, high-power fiber lasers or sensors. These key applications rely on the qualities of silica glass: mechanical and chemical stability, high optical damage threshold, low cost, etc. New lasers and amplifiers based on rare-earth (RE)-doped silica optical fibers need improved spectroscopic performances : gain curve engineering, photodarkening, spectral coverage, etc. In this context, a route of interest consists of embedding the RE ions within nanoparticles of composition and structure different from those of silica. In this work, we study the properties of silica-based, MCVD-prepared fibers using LaF3:Tm3+ nanoparticles. The nanoparticles with 10-20 nm of diameter were produced by precipitation methods and were incorporated by solution doping. Through SEM analyses on preform and fiber, nanoparticles were observed across the core. As F-ions evaporate, the new phase is a La-rich silicate and its composition will be discussed based on the comparison with similar samples prepared by sol-gel. The first e-folding time of the 810-nm emission band (3H4 level) increases with the concentration of La. The best compromise between lifetime enhancement and optical attenuation corresponds to 58 μs and 0.05 dB/m, respectively. Yet, to further improve the optical properties, there is a need to limit Rayleigh scattering induced by the presence of nanoparticles. In the frame of these optical losses reductions, we propose to take advantage of the fiber drawing to tailor the size of nanoparticles. Indeed, we will report evidences that this step permits the deformation and break-up of elongated particles. The possibility of considering break-up as a way to implement size tailoring of nanoparticles will be discussed. These results clearly offer new possibilities for the control of the luminescent properties and the development of optical fibers with augmented properties.